The goal of this program is to study etiologic factors and pathogenetic mechanisms in renal diseases in childhood and to explore factors involved in renal allograft rejection. In addition to studying patients, appropriate models are being investigated. The specific aims are as follows: 1) to investigate the ultrastructural basis for increased glomerular permeability in experimental immunologically induced glomerular disease; 2) to evaluate the structural and immunofluorescence findings in children with the idiopathic nephrotic syndrome and various forms of glomerulonephritis and to examine the relationship of the findings to the course and response to treatment; 3) to investigate immunological mechanisms involved in tubular and interstitial renal disease; 4) to study the nature of the mononuclear cells participating in certain mediated reactions; 5) to investigate abnormalities of the complement system found in several forms of renal disease; 6) to explore mechanisms of immunological tolerance; and 7) to study the immunosuppressive properties of antilymphocyte serum and the immunological reactivity of renal allograft recipients.